Preliminary Study On Biosorbents For Heavy Metals

In the present work, soybean straw was modified with citric acid (CA) to prepare a metal ion adsorbent with good performance. The copper(II) adsorption capability of the adsorbents was investigated, and the effects of various experimental parameters(e.g. contact time, initial pH of the Cu(II) solution, initial Cu²⁺ concentration) was also studied in detail. The adsorption isotherm was got by data fitting. Furthermore, the morphological and chemical characteristics of the adsorbent were evaluated and then the adsorption mechanism was presented.When heated, citric acid will react with the hydroxyl groups on the cellulose to form an ester linkage. The introduced carboxyl groups increase the net negative charge on the soybean straw, thereby increasing its binding potential for metal ions. By spectroscopy and N2-adsorption techniques, we found the porous structure was preserved afer modification. Fourier Transform Infrared (FTIR) spectra of the soybean straw adsorbents show that there are carboxyl groups on the adsorbents.Cu²⁺ concentration was determined by inductively coupled plasma atomic emission spectrophotometry, and then the adsorption capability of the adsorbents was investigated. The adsorption capacities increased when the solution pH increased, and significantly altered beyond pH 5 and reached maximum at the initial pH of 6. Otherwise, The Cu²⁺ uptake increased and percentage adsorption of the Cu²⁺ decreased with the increase in initial Cu²⁺ concentration. The adsorption rates of Cu²⁺ were very rapid during the first ten minutes, and then slowly down. For all the samples with chemical modified, within one hour the Cu²⁺ adsorption achieved equilibrium. For water washed soybean straw without modification (WWSS), the equilibrium was attained after four hours, a much longer time. Freundlich model fited much better than the Langmuir model for Cu²⁺ adsorption data, all the correlation coefficients"r²"were above 0.90. Freundlich parameters indicate that base washed, CA modified soybean straw (CA-BWSS) has the best adsorption capacity. However, Using the Langmuir model, the maximum adsorption capacity of CA-BWSS can be estimated as 0.77 mmol g^-1 or 48.81 mg g^-1.Compared with the unmodified soybean straw, CA modified soybean straw has much better performance. Finally, we can conclude that CA modified soybean straw may be used as an low cost alternate adsorbent for the decontamination of metal-containing eflluents.